A 62-year-old man comes to the office with right arm clumsiness. Physical examination reveals motor weakness involving the right arm and leg. The patient's speech is slurred, and there is drooping of the right lower face. On passive flexion of the right arm, there is initial resistance followed by a sudden release of tension as flexion is continued. A lesion affecting which of the following brain structures is most likely responsible for this patient's condition?

Question

A 62-year-old man comes to the office with right arm clumsiness.  Physical examination reveals motor weakness involving the right arm and leg.  The patient's speech is slurred, and there is drooping of the right lower face.  On passive flexion of the right arm, there is initial resistance followed by a sudden release of tension as flexion is continued.  A lesion affecting which of the following brain structures is most likely responsible for this patient's condition?

Quizplus · Accepted Answer

11ec160b_35b5_2d1f_9249_ef87b1801e40_MD0001_00 This patient has clasp-knife spasticity, which is characterized by initial resistance to passive flexion followed by a sudden release of resistance. This form of spasticity is seen with upper motor neuron lesions and results from a lack of upper motor neuron inhibition on the spinal stretch reflex arc. With passive arm flexion, the extensor muscles are activated by the disinhibited stretch reflex, causing initial resistance that can be overcome with continued flexion. Upper motor neuron lesions can affect any part of the pyramidal motor system (eg, corticobulbar/corticospinal tracts), which runs from the precentral gyrus (primary motor cortex) through the internal capsule to the brainstem and spinal cord. Patients with an internal capsule stroke can have both sensory and motor deficits, but most commonly have pure motor weakness affecting the contralateral arm, leg, and lower face as well as clasp-knife spasticity, hyperreflexia, and a positive Babinski sign. (Choices A, D, and E) The caudate nucleus, putamen, and globus pallidus (ie, basal ganglia) are part of the extrapyramidal motor system, which regulates both voluntary and involuntary motor function (eg, posture, muscle tone, prevention of erratic movements). Lesions to these structures can result in motor dysfunction, including chorea (ie, random, jerky, uncontrollable movements), tremor, bradykinesia, or rigidity, as well as changes in cognition and behavior. (Choice C) The insular cortex (insula) plays a role in consciousness and emotion (along with the limbic system), autonomic nervous system control, and awareness of visceral sensations. Educational objective: Upper motor neuron lesions (ie, internal capsule stroke) cause contralateral weakness with clasp-knife spastic rigidity, hyperreflexia, and a positive Babinski sign. These lesions damage the pyramidal motor system (eg, corticospinal tracts), which runs from the precentral gyrus (primary motor cortex) through the internal capsule to the brainstem and spinal cord. __________ References: Pathology of lacunar ischemic stroke in humans--a systematic review. (http://www.ncbi.nlm.nih.gov/pubmed/22329603)

A 62-Year-Old Man Comes to the Office with Right Arm